For anyone else out there who has Vikunja deployed using docker, please take note that the vikunja/api and vikunja/frontend containers have been combined into a single vikunja/vikunja container as part of release 0.23. You will have to update your compose files to reflect this change as part of the upgrade. I just went through this and it went very smoothly. The directions on the linked webpage make it fairly easy. Happy self-hosting!